DNA remains an underrepresented target for small molecule therapeutic agents. There is mounting evidence to indicate that non-B DNA structures play prominent roles in gene expression and in the function of telomeres. Targeting these structural elements is an attractive and innovative strategy for the development of new therapeutic agents. The use of small molecules in such an antigene strategy is promising for many reasons. Targeting the gene before its amplification to produce multiple mRNA and protein molecules is advantageous because there are fewer targets to hit. In addition, is easier to manipulate small molecules (rather than therapeutic DNA or RNA molecules) chemically to optimize binding and pharmacological properties. We seek renewal for our innovative and highly productive program to develop an integrated virtual and actual screening platform for the discovery of new lead compounds that bind selectively to unique DNA structures of biological significance. Progress during the initial funding period was outstanding, and we achieved most of the specific aims proposed in our initial proposal. We have discovered several compounds that bind selectively to particular quadruplex structures, a target of intense current interest. We propose studies that will continue to develop and optimize the integrated screening platform. During the next funding period, we will focus on the discovery of lead compounds that bind selectively to biologically important quadruplex and DNA-RNA hybrid structures. In order to do this, we will develop structural models for complex quadruplex structures using a novel approach that integrates molecular dynamics simulations with rigorous experimental validation. We will characterize the biophysical and functional properties of the novel quadruplex binders we have discovered during the initial funding period. Specific aims include: 1. Development and refinement of the virtual screening platform. 2. Development of higher-throughput assays for ligand binding. 3. Discovery of lead compounds that bind to functionally important nucleic acid structures. 4. Biophysical and biological characterization of novel G-quadruplex binding agents discovered during the initial funding period. The proposed studies will deliver an improved integrated platform for the discovery of novel lead compounds and a thorough characterization of several newly-discovered quadruplex binders with unique chemical scaffolds.